The present invention relates to a seal material for use in a scroll type compressor. More particularly, the present invention relates to a tip seal for use in a scroll type compressor using a carbon dioxide gas as a refrigerant.
A scroll type compressor comprises a fixed scroll 1 and a movable scroll 2 that are eccentrically engaged each other in a spiral-shaped lap wall 3, as shown in FIG. 1 illustrating a cross-sectional view of a compressing mechanism. The fixed scroll 1 has a panel board 1a and a spiral-shaped lap 1b that is disposed vertically on the panel board 1a. The movable scroll 2 has a panel board 2a and a spiral-shaped lap 2b that is disposed vertically on the panel board 2a. The fixed scroll 1 and the movable scroll 2 are engaged eccentrically each other to form a compression space 4. The movable scroll 2 is revolved around an axis of the fixed scroll 1, whereby the compression space 4 moves to a spiral center to compress a gas.
To assure sealing properties of the compression space 4, grooves are formed at end faces of the laps of the fixed scroll 1 and the movable scroll 2 along an extended spiral direction. Tip seals 5 are spiral-shaped seal members slidably contacted with opposing panel boards, and are included in the grooves. FIG. 2 shows a perspective view of the tip seal 5.
As shown in FIG. 2, the tip seal 5 is in a spiral shape, and has a rectangle profile. The tip seal 5 is included in the groove of the end face of the lap with a space, and floats from a bottom of the groove toward the opposing panel board by a gas pressure between the groove and the opposing panel board to seal spiral walls.
The scroll is made of, for example, an aluminum alloy to lighten the weight, other than a steel product. The sliding contact surface of the scroll is often surface-treated including hard chromium plating, kanigen plating, alumite treatment, and tuframe treatment in order to improve wear resistance.
It urges that the refrigerant should be changed from conventional flon such as R12 and substituted flon such as 134a to a carbon dioxide gas from the viewpoint of solving a recent global warming problem. When the carbon dioxide gas is used as the refrigerant, it requires a higher gas compression pressure as compared with the case that the conventional refrigerant is used. Accordingly, the tip seal must be withstood a temperature of 120xc2x0 C. or more, in some cases, 150xc2x0 C. or more, and a discharge pressure of 8 MPa or more, in some cases, 10 MPa or more. In the case of the conventional flon and substituted flon, it is enough for the tip seal to withstand a temperature of 120xc2x0 C. to 150xc2x0 C., and a discharge pressure of 2 to 3 MPa.
Mineral oils used as a refrigerating machine oil are replaced with an ester oil, a polyalkylene glycol oil (hereinafter referred to as xe2x80x9cPAG oilxe2x80x9d), and a carbonate oil. The tip seal is required to withstand these oils.
Conventionally known materials of the tip seal for flon and substituted flon include a tetrafluoroethylene resin (hereinafter referred to as xe2x80x9cPTFExe2x80x9d) and an aromatic polyether ketone based resin (hereinafter referred to as xe2x80x9cPEKxe2x80x9d) containing a melt fluororesin, both of which are disclosed in Japanese Examined Patent Publication No. 7-030747, a PEK composition containing a copper alloy as disclosed in Japanese Examined Patent Publication No. 7-122015, a PEK composition containing a carbon fiber, PTFE, and metal powder as disclosed in Japanese Examined Patent Publication No. 7-069015, and a PEK composition containing a polyphenylether oil as disclosed in Japanese Examined Patent Publication No. 7-098897. Also, there is known a PEK composition containing a liquid crystal polyester resin as disclosed in Japanese Laid-Open Patent Publication Nos. 8-267613, and 9-20883.
In the scroll type compressor using the carbon dioxide gas as the refrigerant, the tip seal must be withstood a temperature of 120xc2x0 C. or more, in some cases, 150xc2x0 C. or more, and a discharge pressure of 8 MPa or more, in some cases, 10 MPa or more. The conventional seal materials have undesirably insufficient load-bearing properties, wear resistance, and non-damaging properties for a mating material. Even if the materials have sufficient load-bearing properties and wear resistance, there cannot be provided sufficient melt flowability to form the tip seal.
For example, the tip seal materials disclosed in Japanese Examined Patent Publication Nos. 7-030747 and 7-122015 have poor load-bearing properties since the loading materials have no reinforcing effects.
The tip seal material disclosed in Japanese Examined Patent Publication No. 7-069015 can have sufficient load-bearing properties, but has less melt flowability. The tip seal with a small cross-sectional area cannot be formed therewith. In the scroll type compressor, when a lubricating oil is insufficient, and cannot be provided on a sliding surface under high speed and high pressure, metal powder is seized. In particular, when the scroll member that is contacted slidably therewith is made of aluminum alloy, the aluminum alloy may be damaged significantly.
The tip seal material disclosed in Japanese Examined Patent Publication No. 7-098897 is separated and decomposed when the tip seal is formed, which leads to unstable melt flowability. There cannot be provided stable load-bearing properties and wear resistance.
The tip seal materials disclosed in Japanese Laid-Open Patent Publication Nos. 8-267613 and 9-20883 may have lowered strength because of a combination of the liquid polyester resin and the PAG oil. Such tip seal materials cannot be used for the scroll type compressor using a carbon dioxide gas as the refrigerant and having the discharge pressure of 8 MPa or more, in some cases, 10 MPa or more.
An object of the present invention is to provide a tip seal and a seal material for use in a scroll type compressor using a carbon dioxide gas as a refrigerant; the tip seal and the seal material having excellent load-bearing properties, wear resistance, non-damaging properties for a mating material, and formability.
According to the present invention, a tip seal for a scroll type compressor with a discharge pressure of 8 MPa or more, comprises a resin composition that is molded into a spiral shape, and that contains an aromatic polyether ketone based resin as a main component, and at least a carbon fiber and a tetrafluoroethylene resin. The scroll type compressor uses a carbon dioxide gas as a refrigerant.
The resin composition is a PEK composition containing at least 5 to 30% by volume of the carbon fiber and 1 to 30% by volume of the PTFE resin based on the whole resin composition.
The PEK composition further contains 1 to 20% by volume of an inorganic compound having Moh""s hardness of 3 or less based on the whole resin composition.
According to the present invention, a carbon fiber is included as a fibrous reinforcing material, thereby improving load-bearing properties and wear resistance of the PEK composition. In addition, PTFE is included therein as a solid lubricating material, whereby no seizure occurs, and low frictional properties are added to the seal material if the lubricating oil is insufficient.
An addition of the inorganic compound having Moh""s hardness of 3 or less reinforces fiber-to-fiber microscopically, and can improve wear resistance synergistically. When the mating material that is contacted slidably is made of aluminum alloy, the aluminum alloy may be less abraded and damaged because the inorganic compound having Moh""s hardness of 3 or less is smaller than the carbon fiber, exists on the sliding surface at high density, and accommodates major shear at the sliding surface.
The load-bearing properties and the wear resistance are improved by using the above-described PEK composition. When the resin has the predetermined melt viscosity, there is provided sufficient melt flowability for forming a tip seal with a small cross-sectional area. Thus, the tip seal and the seal material of the present invention are suitable for use in the scroll type compressor made of the aluminum alloy utilizing a carbon dioxide gas as the refrigerant.